Apparatus for testing the surface hardness of construction materials



1954 E. o. SCHMIDT APPARATUS FOR TESTING THE SURFACE HARDNESS 0F CONSTRUCTION MATERIALS Flled May 29, 1951 INVENTOR. ERNST 0. SCHMIDT ATT RNEY Patented Jan. 5, 1954 APPARATUS FOR TESTING THE SURFACE HARDNESS OF CONSTRUCTION MATE- RIALS Ernst 0. Schmidt, Basel, Switzerland, assignor to Arthur R. Anderson, Springdale, Conn.

Application May 29, 1951, Serial No. 228,808

4 Claims. 1

The invention relates to apparatus for testing the surface hardness of construction materials such as metal, concrete, artificial stone, ceramic products, etc. Apparatus constructed in accordance with the invention comprises a frame adapted to be placed against the surface to be tested, a hammer movable in the frame for impact against such surface, and an indicator assov ciated with the frame to measure the intensity of rebound of the hammer after impact. The hammer is propelled by energy stored therein as by means of a spring or other resilient element arranged between the frame and the hammer.

Experiments have shown that apparatus according to the invention makes possible a rapid 3 and easy testing of surface hardness of construction materials, whether the surfaces be horizontal, vertical, or inclined, whereby the inclination of the test surface requires at most only a correction factor applied to measured rebound intensity for a given inclination.

.The hardness of a given material generally bears a relationship to other physical properties of the material, which, within a certain deviation can be determined experimentally. For example, the apparatus has been developed in a form for determinin the compression strength of concrete in construction, and has proven itself for this application.

In the drawings which further illustrate the invention in one of its preferred forms:

Fig. 1 is a vertical longitudinal cross-sectional view.

Fig. 2 is a cross-section through A-A of Fig. 1.

A housing I of tubular form has at one end a flange 2 with three projections 3 which provide points of support on the surface to be tested. Within housing I a test hammer 4 is arranged for movement along the tube axis. It has a square cross-section with corners rounded so that the inside of the tube serves as a guide. A longi tudinal slot 5 running the length of the lower side of the tube is provided, opposite to which a shorter longitudinal slot 6 is provided. On the outside of tube I a longitudinally slidable trigger 1 is provided with an opening 8 through which the operators finger can be inserted. Trigger 1 is provided at the right-hand end With a throat piece 9 which is attached to trigger 1 through slot 5 from the inside of tube I, providing a guide for longitudinal motion in slot 5.

At the left-hand end of trigger I a catch II is provided so that it can engage the shoulder I2 of the hammer 4 when depressed inwardly 2 through slot 5. For this purpose the throat o catch II is made somewhat deeper than the wall thickness of tube I, allowing a slight rotation of trigger I as indicated by arrow I3, enabling catch II to be disengaged from shoulder I2.

The hammer 4 is hardened steel and is provided with a spherical head M at the front end to give a central zone of contact during impact with the test surface. At the rear end of the hammer 4 a cross pin I5 is located so that it travels freely in the two diametrically opposite longitudinal slots It in tube I. On each end of pin I5 grooves I? are provided to take tension springs .13 which are attached at their other ends to flange 2. Parallel to tube I immediately outside longitudinal slot 6 a longitudinal bar I9 is provided with attachment to flange 2 at one end and to cap piece 20 at the other end. On bar I9 a longitudinally movable pointer 2| is provided with a slight friction against free sliding. Pointer 2| can be engaged with a rotatable catch 22 through slot 6. Catch 22 is located in a fork in the end of hammer A, attached perpendicularly to the axis of tube I by pin 23. Catch 22, when viewed in Fig. 1 is rotatable only in a clockwise direction on pin 23.

A scale 24 is located on the outside of tube I parallel to slot 6 adjacent to the edge of pointer 2|.

To test, for example, the surface of a concrete wall, the apparatus is placed horizontally as seen in Fig. 1 against the selected test location so that it rests on projections 3. The apparatus is held in position by grip 25 with one hand, and with the thumb of the free hand catch 22 is depressed in the direction of arrow 26, rotating on pin 23 to move under pointer 2|. Then a finger of the free hand is placed in opening 8 of trigger I, pressing it against the tube I so as to engage catch II with shoulder I2 of the hammer 4. Next the trigger 1 is drawn in the direction of arrow 2'! to the position 1' indicated by the dotdash lines on Fig. 1. Hammer 4 is thus moved against tension springs I8. Next trigger 1 is moved in the direction of arrow I 3 allowing catch II to disengage shoulder I2 of hammer 4, and the energy stored in springs I8 catapults hammer 4 toward the test surface, against which the spherical head I4 of hammer 4 impacts with a definite predetermined energy. The intensity of rebound of hammer l is dependent on the hardness of the test surface of the material being tested. Catch 22 at the instant of impact swings outward to the position shown in Fig. 1, and on the return stroke of hammer 4 it engages sliding J pointer 2|, moving it along bar l9 to indicate on scale 24 the amount of rebound travel of hammer 4, giving a measure of the hardness of the test surface.

To make further test measurements, pointer 21 is manually moved back each time to the original positionso as to be engaged by catch 22 on the rebound othammerl.

Although the drawing shows the guide for the longitudinal movement of the hammer to be provided by the tubular housing, other. methods of guiding the hammer, such asitracks could be employed. Moreover, means other than springs [8 could be used for propelling the hammer 4. For example, the force 'of -gravity,.-through a pendulum-lever arrangement, could furnish a propelling force to the hammer. The hammer could also be arranged as a piston designed to be longitudinally movable in a cylinder closed at one end. By moving the piston against the closed-end: of the: cylinder, a pneumatic-pressure couldbebuilt unto. be used as aprope'lling: force.

Under certain circumstancesit is advantageous This insert ingtto facilitate itsinterchangea "ty Moreover, the hammer head can be rigidly, but removaolyconnected to the body of the hammer,

allowing a choice of hammer head typesto variations in. conditions or materials under test.

Lolaim: all.,Apparatusfortesting the surface hardness ofconstruction materials comprising a frame, an element mounted on the frame adapted to be ;placed,against a surface to-oe tested, ahamrner movablelongitudinally in said frame for creating impaot against the surface to be tested, and a propelling resilient. element between the frame and hammer to propel the hammer, movement Ofuf/hehammer longitudinally in a horizontal .planeroeing. controlled entirely bysaid propelling resilient element and an indicator fixed to the frame to. measure the intensity. of rebound of the "hammer rafter. impact.

J2..Apparat.usaccording to claim .1 inwhich said frame comprises a tubular housing to guide the hammer, said housing having a longitudinal slot, and an operating trigger slidably mounted in said housing and extending through the slot for engagement with the hammer to move it longitudinally against the action of said resilient element, said trigger-being? movable into a position in which the hammer is disengaged therefrom.

3. Apparatus for testing the surface hardness .ofi constructionmaterials comprising a frame adapted tdbie placed against a surface to be tested} a hammer movable longitudinally in said frame to impact against the surface to be tested, a resilient element between the frame and hammer'topro'pelthe hammer, said frame comprising a tubular housing to guide the hammer, said housing having a longitudinal slot, a longitudinally movable pointer slidably mounted outside of said housing adjacent said slot for movement parallel thereto, ascale on the housing over which the pointer -moves, and; a catch pivotally mountedon the hammer, said catch-arranged-to swing into a position in which it extends; through said slot for engagement with said pointer to move-iton reboundof the hammer.

4: Apparatus for testing the surface hardness of construction materials comprising aframe,

face, and an indicator scale fixed to the frame to show the intensity of reboundas measuredtby said resilient element.

ERNST 0-. SCHMIDT.

References Cited in'the file of 'this patent UNITED STATES PATENTS Number Name Date 1,4463620 Hall Feb; 27-, 1923 1,708,262 Davis-1r. r Ap-r.= 9 ,:1929 2549-135 1 2 Moore a Den 20, 7-1949 FOREIGN PATENTS Number Country Date 129,037 Switzerland: Dec. 1, 1928 

